Penelope has been drinking coffee for the past 10 years. She says she needs the caffeine just to get through the day. Today, she has not had any coffee and has a severe headache, fatigue, and shakiness. Penelope is most likely dependent on caffeine.

Penelope is most likely suffering from withdrawal symptoms as a result of dependent on caffeine.

Explanation:

Coffee like every other stimulant out there is a central nervous stimulant which enhances concentration, increases the metabolisim of the body and boost the mood of an individual. The higher the quantity of coffee taken by an individual, they higher the dependence of the individual to the the stimulant as a result of the caffeine which is a constitutant of coffee.

Just like drugs, when someone refuses to take coffee after his body has grown accomstomed to it would lead to violent reaction of his body system as a result of the body system withdrawing from it. This is known as a withdrawal sysptom.

With regards to Penelope, the severe headache, fatigue and sakiness which she experienced as a result of not taking coffee in a day are known as withdrawal symptoms after her body system has become dependent on caffeine (As a result of drinking coffee for the past 10 years).